Major findings
The current study showed the clinical significance of native T1 mapping in patients with newly diagnosed DCM. There were no significant differences in LV volumes and the presence of LGE between patients with recovered EF and those without. However, patients without recovered EF had a higher native T1 value than those with recovered EF. Furthermore, both the native T1 value and the presence of the native T1 high region were independently associated with recovered EF. The native T1 high region had an incremental prognostic value for predicting recovered EF. Thus, the native T1 high region and the native T1 value might be important markers for predicting recovered EF in patients with DCM.
High Native T1 Value And Lvef Recovery
A high native T1 value indicates oedema (increased tissue water content caused by different factors including inflammation) and high interstitial components (e.g. fibrosis and amyloid deposition).(9) In the current study, the non-recovered EF group had a significantly higher native T1 value than the recovered EF group. Hence, fibrosis progression was correlated with the presence or absence of LVEF improvement. These results are consistent with those of two previous studies, which reported that patients without LVEF recovery had a significantly higher native T1 value and ECV than those with LVEF recovery.(14)(22) In contrast, another study found that ECV and T2 values but not native T1 values were associated with LV reverse remodelling.(23) This discrepancy might be explained by differences in the definition of LVEF recovery and the study cohort. For example, this study only included 58% of patients with newly diagnosed DCM. However, in the current study, all patients were newly diagnosed with DCM. This difference might affect differences in the prognostic factors of LVEF recovery because the HF duration is a key factor of LVEF recovery.(24)
Both native T1 and ECV fractions are correlated with histological collagen volume fractions. ECV quantifies the interstitial uptake of gadolinium contrast agent relative to the plasma. Native T1 mapping can be an effective alternative option to ECV measurement if a shorter scan time and non-contrast material requirements are considered.(12) Thus, native T1 mapping can be a more convenient method for identifying patients with or without LVEF recovery after GDMT.
Native T1 High Region And Lge
LGE is the gold standard method for assessing focal myocardial damage representative of fibrosis.(25) LGE is associated with poor LVEF recovery in patients with DCM.(6) Conversely, similar to the current research, some studies showed that LGE was not a predictor of LVEF recovery.(22)(26) The reason for this discrepancy is unclear. However, the differences in cohorts and the number of events might be a cause.
In the current study, the native T1 high region was associated with LVEF recovery. Two previous studies revealed that the native T1 value of the segments with LGE was higher than that of the segments without LGE in patients with DCM.(27)(28) However, the association between T1 values per segment and the fraction of segments with LGE were modest.(27) In our research, the native T1 high region was observed in the segments without LGE. Therefore, the native T1 high region reflects focal myocardial alterations. However, it is not necessarily consistent with LGE. This discrepancy might be attributed to the fact that LGE may primarily indicate myocardial fibrosis and a high native T1 represents oedema and high interstitial components.(9) Moreover, Dass et al. showed that T1 mapping and LGE measurement were partly overlapping. Nevertheless, there were distinct myocardial pathologies.(27) Furthermore, T1 mapping facilitates direct myocardial signal quantification on a standardised scale. The advantages of T1 mapping can allow a better characterisation of myocardial tissue compared with LGE.(25) Therefore, the native T1 high region is more effective in identifying focal myocardial damage than LGE.
In a previous study, the native T1 value significantly decreased after GDMT. This finding indicates reduced collagen volume fraction and serum myocardial collagen accumulation index in patients with DCM after GDMT.(23) The current research did not assess changes in the native T1 value and the native T1 high region over time. Hence, further studies on this topic should be performed.
Clinical Implications
Native T1 mapping can be performed on all patients eligible for CMR imaging because it does not require gadolinium contrast agents. In addition, the native T1 high region had an additive predictive value for predicting LVEF recovery. In relation to this reason, it might be helpful to focus on the native T1 value and the native T1 high region in determining appropriate treatment strategies in patients with newly diagnosed DCM.
Study Limitations
The current study had several limitations that must be acknowledged. First, this was a single-centre study with a limited number of patients. This could have resulted in patient selection bias and a lower statistical power. Second, only patients undergoing CMR imaging were included in the analysis, which could have posed a risk of bias. Third, the statistical power was limited because of the small number of events. Fourth, T1 mapping images of LV were acquired only at the mid-ventricular level. Therefore, the whole LV myocardium could not be evaluated.